See attachment for screenshot. Load the Privacy and Security panel in prefs (a few other panels are affected too) and you'll see that there are text passages inside titledboxes, but no buttons. Drag another window over the top of the pref window and the invalidated region is repainted correctly, and the buttons are visible. Looks like a painting bug.
There's been a bunch of these lately, in pages/sidebar/prefs/etc, suspect imagelib, reassigning to pav.
sounds to me more like the view manager than iamgelib.
*** Bug 77183 has been marked as a duplicate of this bug. ***
I no longer see painting issues in the pref panels with 2001042920 build on WINNT. Marking WORKSFORME.
Marking verified works for me in the June 4th build.